energy
Energy is a property of matter that is defined as the ability to do work. The concept of energy is useful for explaining and predicting most natural phenomena, and it is the foundation for an understanding of biology. All living organisms need energy to grow and reproduce. However, energy can never be created nor destroyed. Energy can only be transformed. That is, energy is always conserved. This is called the law of conservation of energy . Therefore, organisms cannot create the energy they need. Instead, they must obtain energy from the environment. Organisms also cannot destroy or use up the energy they obtain. They can only change it from one form to another. Organisms will either use their energy for metabolism or release it to the environment as heat.